As is well known, a subtractive color process comprises reducing exposed silver halide grains by an aromatic primary amine type color developing agent to prepare an oxidation product of the color developing agent and coupling the oxidation product thereof with couplers which form yellow, cyan and magenta dyes in the silver halide emulsion to form color images.
In such a process, as a yellow coupler for forming a yellow dye a compound having an active methylene group is used, as a magenta coupler for forming a magenta dye a compound of the pyrazolone type, pyrazolone benzimidazole type, indazolone type and the like is used, and as a cyan coupler for forming a cyan dye a compound of the phenol type and a compound of the naphthol type are used.
Each coupler is dissolved in a water-insoluble organic solvent having a high boiling point, with an auxiliary solvent, if necessary, and is added to a silver halide emulsion, or each coupler is added into the emulsion as an aqueous alkaline solution. Generally, the former case is preferable over the latter case in terms of light resistance, moisture resistance, heat resistance, granularity and color sharpness.
Each coupler is substantially required to have properties such that the coupler not only forms a dye but also has high solubility for an organic solvent having a high boiling point or for an alkaline solution, high dispersibility and stability in a silver halide photographic emulsion. In addition, the thus formed dye should be fast to light, heat and moisture, its spectral absorption characteristic should be excellent, its transparency should be excellent, its images should be clear and sharp and, importantly, its coloring density and color forming rate should be high.
In order to reduce the cost for treating waste solutions, it is necessary to remove benzyl alcohol which is added at color development. Generally, when a color developing solution contianing no benzyl alcohol is used, it is very common that the coloring properties of a coupler added to a silver halide photographic emulsion, such as the color forming rate and the maximum coloring density, are disadvantageously effected. Accordingly, it is desirable that the coloring properties of a yellow coupler do not depend on benzyl alcohol and that the storage of images is improved. Further, it is required to strictly control the pH condition at color development because a conventional yellow coupler has generally a high dependence on pH. In fact, it is very common that the optimum pH of color development changes with each color developing agent, coupler or a combination of couplers. Therefore, a yellow coupler having less pH dependence is required.
It is known that skeleton structures of a yellow coupler include pivaloylacetanilide type, benzoylacetanilide type, malondiester type, malondiamide type, dibenzoylmethane type, benzothiazolylacetamide type, malonester monoamide type, benzothiazolyl acetate type, benzoxazolylacetamide type, benzoxazolyl acetate type, benzimidazolylacetamide type or benzimidazolyl acetate type couplers. Of these couplers, benzoylacetanilide type and pivaloylacetanilide type couplers are preferred.
Specific examples of the above-described yellow couplers are disclosed in U.S. Pat. Nos. 2,875,057, 3,265,506, 3,408,194, 3,551,155, 3,582,322, 3,725,072, 4,356,258, 3,891,445, German Pat. No. 1,547,868, German Patent Application (OLS) Nos. 2,219,917, 2,261,361, 2,414,006, British Pat. No. 1,425,020, Japanese Patent Publication No. 10783/76, Japanese Patent Application (OPI) Nos. 26133/72, 73147/73, 102636/76, 6341/75, 123342/75, 130442/75, 21827/76, 87650/75, 82424/77 and 115219/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
In order to develop yellow couplers of the .alpha.-benzoylacetanilide type and the .alpha.-pivaloylacetanilide type which meet the above-described requirements, it has been proposed to devise a structure of sulfonamide group to be introduced into the anilide nuclei. However, until now a yellow coupler having all of the above-described desirable properties has not been developed.
Specific examples of yellow couplers of .alpha.-pivalylacetanilide having an alkyl sulfonamide bond, an alkaryl sulfonamide bond, an aralkyl sulfonamide bond, a phenyl sulfonamide bond and an alkoxyphenyl sulfonamide bond at the 5-position, and whose hydrogen atom at an active side is substituted by a phenoxy group having a carboxy group, a nitro group, a 4-benzyloxyphenylsulfonyl group, a 2-alkoxyphenylsulfamoyl group, an alkylsulfamoyl group, a 4-hydroxyphenylsulfonyl group, an alkylphenylsulfonyl group, a phenylsulfonyl group, an alkylsulfonyl group or a cyano group at the 4-position are disclosed in U.S. Pat. Nos. 3,933,501 and 3,894,875.
These yellow couplers do not exhibit satisfactory coupling reactivity in the color developing solution in which benzyl alcohol is removed. Further, a comparatively high active coupler having a 4-hydroxyphenylsulfonyl phenoxy group at its active side is sensitive to changes in pH of the color developing solution. Therefore, the color density of the thus obtained color images is not uniform and the coupling activity decreases with a decreasing ratio of yellow coupler/organic solvent having a high boiling point.
In Japanese Patent Application (OPI) No. 142340/80 a yellow coupler of .alpha.-acylacetanilide containing an alkoxyalkylsulfonamide group at a non-coupling position is disclosed. It is further disclosed therein that an ether bond is introduced into a hydrophobic alkyl group part of an alkylsulfonamide group to increase the hydrophilic property, and that as a result thereof, the coupling activity of the yellow coupler is improved. However, ths thus formed dye does not have light fastness.
Yellow couplers of .alpha.-amylacetanilide having an alkylsulfonamide group which is substituted by a predetermined substituent, such as an alkylthio group, an alkyl sulfonyl group, an acyloxy group, an alkoxycarbonyl group, an amino group, a carbamoyl group, an imide group, a sulfonamide group and the like, are disclosed in Japanese Patent Application (OPI) No. 21738/83. These couplers also do not have light fastness. In addition, these couplers have a low coupling activity.
Yellow couplers of .alpha.-acylacetanilide wherein a nitrogen atom in a sulfonamide group is substituted by a substituent, such as a cyano group, a halogen atom, an alkyl group, an aryl group or a heterocyclic group and the like, are disclosed in Japanese Patent Application (OPI) No. 121126/79. However, these couplers have a low coupling reactivity and the thus formed dye is not fast to light, heat, humidity and the like.
Yellow couplers of .alpha.-acylacetanilide having a halogen atom or an alkyl group at the 2-position thereof having a halogen atom, an alkyl group or an alkoxyl group and having an alkylsulfonamide or an alkylsulfonamide substituted by a phenyl group are disclosed in Japanese Patent Application (OPI) No. 42046/83. However, these couplers have such a serious defect in that the thus formed dye has poor light fastness.
Yellow couplers of .alpha.-pivalylacetanilide having at a coupling position an aryloxy group containing a carbonyl group, a sulfonyl group or a phosphenyl group at an ortho position of the oxygen atom thereof and an alkylsulfonamide group at the 5-position thereof are disclosed in U.S. Pat. No. 4,401,752. The thus formed dye of these couplers has poor light fastness.